Study reveals that BR-319 fueled the smoke crisis in Manaus in 2023

By Fred Santana – From Cenarium

MANAUS (AM) – The origin of the smoke that blanketed Manaus (AM) in the second half of 2023 is directly linked to deforestation and fires along highways BR-319 and AM-254, particularly in the municipalities of Manaquiri, Careiro, and Autazes. The finding comes from a study published in the journal Discover Sustainability by researchers from the University of São Paulo (USP), the Federal University of Amazonas (Ufam), and the National Institute for Amazonian Research (INPA).

The survey shows that air pollution levels exceeded the limit recommended by the World Health Organization (WHO) by more than 20 times. To illustrate, on October 12, 2023, Manaus recorded peaks of fine particulate matter (PM2.5) concentration reaching 314 µg/m³, higher than levels observed in cities like New Delhi, India, known for its chronic air pollution.

To verify the relationship between land use along the highways and air pollution in the Amazonian capital, the research team used atmospheric data from the Amazon Tall Tower Observatory (ATTO), of INPA, located about 150 km northeast of Manaus, toward Pará, as well as sensor data from the Amazonas State University (UEA) to measure PM2.5 particulate emissions, a key indicator of air pollution. The team also used meteorological data from the National Institute of Meteorology (Inmet) and satellite data from the Fire Monitoring Project of the National Institute for Space Research (Inpe).

“The pollution peaks in Manaus were much higher than those recorded in Santarém and occurred earlier, ruling out the hypothesis of smoke transport from the east. Furthermore, winds were practically stagnant over the city, and sensors detected higher concentrations of pollutants precisely south of Manaus, in the direction of the fires in Careiro, Autazes, and Manaquiri, along BR-319. In other words, the crisis originated within Amazonas itself,” said Lucas Ferrante, researcher at USP and Ufam, one of the study’s authors.

“It’s ruled out that the smoke came from Pará because we measured emissions both from that state and from intermediate regions, and they were not proportional to the intensity of the smoke that reached Manaus,” added Philip Fearnside, researcher at INPA and co-author of the study.

Annual smoke crises

According to the authors, allowing the reconstruction works on BR-319 could recreate in Manaus the same scenario already observed in the so-called ‘Arc of Deforestation’, in the southern Amazon, where roads have historically opened paths for land grabbing, agricultural expansion, and systematic burning. The alarming smoke levels of 2023 serve, they warn, as a “warning sign” of what could become recurrent if the project advances.

“The highway facilitates the opening of illegal roads, land grabbing, and cattle expansion, which increase fires. If rebuilt, it will connect Manaus to the same cycle of fire and smoke that already affects the Amacro region [border between Amazonas, Acre, and Rondônia] in southern Amazonas,” warned Ferrante.
“What we saw in 2023 was only a warning: if the road is paved, Manaus could face annual smoke crises, as already happens in the Arc of Deforestation.”

Low-impact alternatives

Given these results, the researchers emphasize that rebuilding BR-319 is unfeasible and, combined with weak environmental enforcement, threatens not only biodiversity and climate stability but also the sustainability of urban centers that depend on the Amazon’s ecological integrity.

The highway, which connects Manaus (AM) to Porto Velho (RO), could affect 63 Indigenous Territories (ITs), five unrecognized communities, and a population of isolated Indigenous Peoples, totaling over 18,000 Indigenous persons impacted by the road. The federal government has announced plans to reach a “definitive agreement” for the road’s paving in September.

Ferrante also stresses that degradation in this region threatens not only Manaus but the entire country. The forest crossed by BR-319 is vital to the “flying rivers”, which carry Amazonian humidity to southeastern and southern Brazil.

“With more deforestation and fire, there will be less rain in those regions, directly affecting agriculture, water supply, and even energy generation. In other words, what happens along BR-319 is not confined to Amazonas, it has consequences for all of Brazil,” he explained.

Instead of road expansion, the researchers advocate for low-impact alternatives for regional development, such as improving river transport. This option, besides being more compatible with the Amazon’s characteristics, would preserve biodiversity and reduce the risk of new smoke crises. For the authors, the 2023 episode illustrates how infrastructure projects that ignore ecological limits can trigger irreversible degradation processes.

Combination with other factors

The 2023 crisis occurred during a severe drought caused by the combination of El Niño and the Atlantic Dipole, which altered wind patterns and reduced regional humidity. This combination made the forest more vulnerable to fire. The data collected by scientists show that the fires closest to Manaus were responsible for the dense pollution cloud that covered the city between September and November that year.

Edited by Marcela Leiros
Translated from Portuguese from Gustô Alves